This invention relates to a contact monitor and annunciator for producing a persistent indication when one of a selected number of monitoring circuits opens due to an abnormal operating condition and which is further able to differentiate an abnormal condition from a momentary power failure.
When transporting perishable cargo in containers, such as mobile trailers, it is necessary to maintain the cargo temperature within a prescribed range to prevent spoilage of the goods in transit. The refrigeration unit that services the container is usually part of the mobile equipment and travels with the container as it is moved from place to place. Climate control can thus be maintained at all times when the container is being transported either by truck, rail or ship.
The containers, particularly when shipped by rail or boat, may remain unattended for relatively long periods of time during which engine related faults can take place. Although the refrigeration equipment is usually shut down immediately upon the detection of a fault, the exact nature of the abnormal condition might not be easily detected. For example, where the fault is caused by an overheating condition or a circuit overload, the cause of the failure will usually abate by the time the shut down is noticed and, if not corrected, reoccur when the equipment is placed back upon the line.
Copending application Ser. No. 497,441 which issued as U.S. Pat. No. 4,498,077, Feb. 5,1985 and Ser. No. 497,460 which issued as U.S. Pat. No. 4,502,084, Feb. 26, 1985, both of which were filed May 23, 1983 and which are assigned to the present assignee, disclose apparatus that is capable of detecting the failure of one of the selected event monitoring circuits and providing an indicator signal that persists after shut down. Both of the disclosed systems are adapted to monitor normally closed contacts in the monitoring circuits and respond to the opening of any one of the contacts to initiate a shut down of the refrigeration equipment. The equipment remains shut down until such time as the operator corrects the fault and resets the faulted circuit. Although the prior art annunciators operate quite well and go a long way toward pinpointing the exact cause of a particular fault, they nevertheless can, under certain conditions, give erroneous information concerning a malfunction. Momentary electrical power interruptions, for example, not caused by any abnormal conditions, can be of sufficient magnitude to open one or more of the monitoring contacts thus giving a faulty indication to the operator. A good deal of time and effort may be spent in trouble shooting the equipment before it is determined that it is in working order.